When they get behind the steering wheel of their car or truck, motorists want a smooth, comfortable, stable ride with sure-footed handling and minimal body roll when cornering. And when the suspension doesn’t live up to their expectations, they usually realize repairs or upgrades may be needed.

The aftermarket sells almost $600 million a year in chassis parts, shocks and struts according to a recent analysis by Frost & Sullivan. But sales should be considerably higher based on studies that have shown many worn parts are not being replaced. Why? Because many motorists don’t realize that suspension parts wear out over time. Springs lose ride height. Shocks and struts lose their ability to control suspension motions. Ball joints, tie rod ends and bushings wear out from the constant pounding mile after mile. Sharp-eyed technicians who know what to look for can usually identify parts that need to be replaced, but your typical motorist usually cannot. Consequently, a lot of potential sales are lost.

When Are Components Needed? When parts wear out, they obviously need to be replaced. The same goes for damaged parts. Postponing needed repairs can be dangerous with some suspension parts. A badly worn ball joint, for example, may pull apart allowing the suspension to collapse. Tie rod ends that separate can cause a loss of steering control.

Most worn suspension parts are found when doing pre-alignment inspections. Nobody can realign worn parts, so it’s important to make sure the steering linkage and suspension are in good condition before any alignment adjustments are made. That includes the springs, too, because spring sag can upset wheel alignment.

Unusual tire wear or a steering or handling problem should also prompt a motorist to have his/her vehicle inspected. But many don’t heed the warnings and keep on driving. It’s the same with a rough, bouncy ride, excessive body roll or sway when driving and bottoming out. Weak shocks and struts can’t control suspension motions and maintain proper traction.

Upgrading Ride Control When the handling or ride control performance of a vehicle fails to meet expectations, it opens the door for repairs and upgrades. Repairs are required when parts are broken, bent, worn or out of specifications. Upgrades, on the other hand, can be recommended if the original shocks, struts or springs are considered to be “inadequate” or “unsatisfactory” for the needs of the vehicle owner.

Some vehicles just don’t ride very well even when the original equipment shocks and struts are in perfect condition. Many older SUVs and trucks fall into this category. The combination of relatively stiff springs, heavy-duty dampers and large wheels and tires is not one that lends itself to a car-like comfortable ride. This is especially true with short wheelbase SUVs and trucks that tend to have a rough, choppy ride.

Many small economy cars also come up short in terms of ride quality and handling performance. The low mass of the vehicle combined with a lightweight strut suspension and rack and pinion steering means there’s little to soak up road feedback and harshness. Owners of these vehicles may want a smoother, softer ride. Many small cars also fail to handle extra weight gracefully, and they may wallow and bottom out when loaded with additional passengers or cargo. A typical complaint from the car’s owner may be a plea for extra weight-carrying ability.

Performance cars with sport suspensions can also be a source of ride control complaints. A rock hard suspension may be fine for taking hairpin turns at high speed and generating impressive lateral acceleration numbers on a skid pad, but an overly stiff suspension can’t handle the rigors of tar strips and potholes of everyday driving. Some vehicle owners may complain of a harsh ride. Others may not mind the punishment and may say the suspension isn’t hard enough. They may want even better handling performance and don’t mind sacrificing their kidneys in the process.

Ride control complaints can also arise whenever there is a mismatch between a vehicle’s suspension and the way the vehicle is used by its owner. If a vehicle is used for towing or off-roading, the suspension and shocks should be set up to handle it.

The key to selling ride control and handling upgrades is to figure out what exactly the customer wants and what’s available to fit his vehicle.

Knowing Your Diagnosing Though counter professionals can’t take customers’ vehicles out for test drives when selling parts, technicians often do test drives to diagnose steering, handling and ride-control complaints. The reason why test drives are often necessary is because motorists don’t always describe their vehicle’s symptoms accurately. What one person may describe as a shimmy, vibration or bouncy ride may have nothing whatsoever to do with ride control. The real problem may be an out-of-balance wheel, bent rim or too much runout in a tire. So it’s important to accurately diagnose the problem before any repair or upgrade recommendations are made.

It’s also important to remember that the suspension and steering are interconnected systems. Problems with one can often affect the other. A weak shock absorber, for example, may do little to dampen bumps, allowing excessive feedback through the steering linkage to the driver. The driver may think he has a steering problem, when in fact the real problem is poor ride control. Likewise, a driver may experience poor steering return or find the steering takes extra effort. Again, he may think this indicates a steering problem, but the real cause may be a bad upper strut bearing.

Something else that should be checked is ride height. More than half an inch difference side to side may indicate weak springs or another suspension problem. Ride height measurements front and rear should also be compared to the specifications in a reference manual (which will also show where these measurements are to be taken). If ride height is at or less than the minimum specified, the springs may be sagging (and new springs should be installed).

With ball joints, replacement is required if wear exceeds factory limits. Inspection procedures and specifications vary from one application to another, so it is important to refer to a ball joint specification chart for the particulars. Many load-carrying, tension-type lower ball joints on General Motors and Ford rear-wheel-drive applications have a built-in wear indicator to show how much wear has taken place inside the joint. This same type of joint is also used in the rear suspension on some of GM’s big front-wheel-drive cars (Cadillac, Buick and Oldsmobile).

Load-carrying ball joints usually wear faster than their unloaded counterparts. Consequently, the lower ball joints on an SLA suspension typically wear out before the upper joints wear out. Symptoms of worn ball joints include front wheel shimmy at low speed, steering wander, clunking noises from the front suspension and camber (shoulder) wear on the front tires.

When one joint is badly worn, chances are its companion joint on the opposite side will also be worn or near the end of its service life. The other joint may still be marginally within specifications, but replacing both joints at the same time is a good idea (though not required).

Some ball joints are difficult to replace because they are pressed into the control arm. Other joints may require the removal of mounting rivets or the complete replacement of the control arm, which means you may need additional tools (bushing tools, ball joint separator, etc.) to replace the joint.

Bounce Test Some industry experts say a traditional bounce test is not very accurate at diagnosing weak shocks or struts. A test drive is a much better indication of the damper’s true condition. Even so, a simple bounce test will often reveal shocks and struts that may need to be replaced.

To do a bounce test, rock one corner of the vehicle up and down several times by pushing down on the bumper or fender, then release it. If the suspension continues to rock up and down more than once, the dampers aren’t doing much to control the suspension. Next, check the odometer. If the shocks have more than 50,000 miles on them, or the struts have more than 75,000 miles on them – the shocks and/or struts should be replaced.

Inspection Points Because the damping characteristics of shocks deteriorate gradually over time, the decline in ride control often passes unnoticed. That’s why shocks and struts need to be inspected periodically, and if possible, subjected to a road test or a bounce test to see if they’re still capable of doing an adequate job. If not, then it’s time to replace them.

Worn shocks and struts can be replaced with a variety of standard or upgrade options. Heavy-duty shocks/struts generally have a larger piston bore and are good for towing. Premium gas-charged shocks/struts can make a noticeable improvement in handling and cornering on vehicles that are not originally equipped with such units. For this reason, gas dampers should be recommended for all applications.

Special high-pressure gas struts and monotube and dual-tube shocks are also available for drivers who want the ultimate in handling performance. Adjustable dampers, as well as electronic shocks and struts, are also available for applications that require these types of units or drivers who want the ultimate setup.

Tips For Installation Most shocks are fairly easy to replace, but struts can be tricky. On older import vehicles that have cartridge-style struts, it’s not always necessary to completely remove the struts to replace the cartridges. There may be enough clearance to swing the top of the strut out from under the fender once the upper mount is unbolted. On some, a spanner wrench or pipe wrench is needed to remove the body nut from the strut. On others, the cartridge can be replaced from above with the strut in place once the upper bearing plate has been removed.

When installing a new cartridge in a rebuildable strut, about three ounces of ATF must be poured into the strut housing to aid heat transfer from the cartridge. Some strut cartridges require spacers or washers under the body nut when the unit is reassembled.

Replacing MacPherson struts requires the use of a spring compressor to remove the spring from the old strut and to install the new spring. Marking the camber bolts at the bottom of the strut and the mounting bolts at the top is recommended, but won’t necessarily eliminate the need to realign the wheels after a new strut has been installed. Alignment should always be checked and readjusted to specifications after the new struts are installed. This is not necessary when replacing shocks.

If brake lines have to be opened during strut replacement, the brake lines will have to be bled afterwards to remove air.

Another part that may need to be replaced when changing a strut is the upper bearing plate. The plate supports the weight of the vehicle and serves as the upper steering pivot. A bad bearing plate can cause steering stiffness, noise and poor steering return (memory steer).